It is known to control an internal combustion engine based on a signal from a crank sensor or crank position sensor in order to properly time engine control events such as fuel injector timing and spark ignition timing. A common way to determine crank position is to equip the engine with a 58-tooth crank wheel, and a crank sensor configured to detect when a tooth of the crank wheel passes by the sensor and output a corresponding crank signal. The crank signal is typically monitored by an engine control unit (ECU), and used by the ECU to operate, for example, a fuel injector or an ignition module.
If the crank sensor becomes damaged, or the crank signal received by the ECU becomes inaccurate or unreliable, the ECU should to be configured to determine that there is a problem with the crank signal. United States Patent Application Publication Number 2009/0265079 published Oct. 22, 2009 by Kondo and assigned to Denso Corporation describes a way to detect a problem with the crank signal if the time interval between successive crank pulses is excessive. However, such a time based approach is problematic because it may not detect an occasional missing pulse, and so may not be able to detect an intermittent crank signal.